This study is designed to validate the reliability and reproductibility of nasal potential difference measurements in patients with cystic fibrosis (CF) and normal individuals prior to applying this technique as an outcome measurement in clinical trials. This procedure measures the electrical voltage at the surface of epithelial cells lining the inferior turbinate (inside the nose) and their response to certain chemical stimuli. These small voltages reflect sodium and chloride transport and are characteristically different in CF patients compared to normal individuals. It is postulated that such measurements will be useful in demonstrating the efficacy of pharmacological agents directed at normalizing electrolyte transport in airway epithelial cells.